Ozone has become increasingly important in the purification or disinfection of water supplies, as well as the treatment of waste water streams or sewage treatment.
Ozone is generally produced in a corona discharge by the passage of an oxygen-containing gas, such as air, oxygen-enriched air, or pure oxygen through the discharge region. The corona discharge is produced by an electric discharge field between two electrodes of different electrical potential.
Early attempts at providing commercial quantities of ozone utilized flat plate electrodes positioned adjacent one another with a discharge space there between. An example of such an ozone generator is shown in U.S. Pat. No. 2,822,327. In addition, that patent also shows the more popularly used present day ozone generator structure wherein an inner tubular electrode is placed concentrically within an outer tubular electrode.
Ozone generators have been constructed wherein the inner and outer electrodes comprise metal tubes. Such a structure is demonstrated in U.S. Pat. No. 3,730,874. This patent has a dielectric tube placed between the outer and inner metallic electrodes. A cooling chamber is located between the dielectric tubular member and the inner metallic electrode. The coolant which is supplied to the space between the inner electrode and the dielectric member is taught to be water which acts as an electrical ground for the inner electrode. The spaced coolant chamber is designed to assure flow of liquid coolant near the surface of the inner electrode.
Alternately, it has been contemplated to cool an ozone generator by the use of cryogenic fluids. In U.S. Pat. No. 3,921,002, an ozone generator is cooled by the utilization of liquid oxygen. The liquid oxygen is maintained inside the inner electrode while gaseous oxygen is circulated between the inner and outer electrodes and converted to ozone. Because of the very low temperature of the liquid oxygen, the ozone, as it is formed, is liquefied.
Ozone generators have been contemplated wherein the outer and inner electrodes are individually cooled by a liquid coolant. In U.S. Pat. No. 4,234,800, an ozone generator is shown in which the inner ground electrode is cooled by a flow of water through the entire void space inside the tubular ground electrode. The outer high voltage electrode is cooled by oil which flows between the outer electrode and the generator's outer superstructure. Such a system requires two separate coolant circulation systems.
The operation of ozone generators creates significant levels of heat due to the formation of ozone from oxygen and due to the electric current flowing through the electrodes of the generator and forming the corona discharge. Excessive temperature created by this heat in an ozone generator hampers the efficient production of ozone by decomposing the product ozone shortly after its formation. Excessive temperature or excessive variation in temperature also diminishes the life of the ozone generator itself, particularly the structurally weak dielectric elements, but to a lesser extent, the electrodes also may be adversely affected by excessive temperature during operation. The prior art has attempted to reduce the occurrence of excessive heating in ozone generators by the introduction of various liquid coolants into the areas surrounding one or both of the ozone generator electrodes. However, cooling capability of a liquid coolant supplied to the generally large areas between the generator containment walls and the nondischarge surfaces of electrodes suffers from the low heat transfer capability resulting from the flow characteristics of the liquid near the surfaces of such electrodes. As liquid coolant flows through a conduit or its flowpath in the generator, a reduced flow rate is experienced at the outer areas of the liquid flow due to frictional forces with the conduit or generator surface. At the core of liquid flow, the flow rate remains high because of the reduction of frictional forces. Attempts have been made to increase the relative flow of coolant near the electrode surface to create turbulent flow in order to enhance heat transfer capability by the reduction in size of the space between the electrode and the containment wall for the coolant flow. However, this solution requires additional apparatus and incurs the potential for arcing across reduced dimension spacing between electrode and generator structure. The present invention overcomes the drawbacks of the prior art and efficiently resolves the problem of over heating or excessive temperatures by the use of a unique coolant system having increased heat transfer capability.
Additionally, the present invention overcomes the problem of weak structural integrity of the dielectric elements in an ozone generator.